Crucial size effects of atomic-layer-deposited Pt catalysts on methanol electrooxidation

Mesokinetics as a Tool Bridging the Microscopic-to-Macroscopic Transition to Rationalize Catalyst Design

Heterogeneous catalysis is the workhorse of the chemical industry, and a heterogeneous catalyst possesses numerous active sites working together to drive the conversion of reactants to desirable products. Over the decades, much focus has been placed on identifying the factors affecting the active sites to gain deep insights into the structure-performance relationship, which in turn guides the design and preparation of more active, selective, and stable catalysts. However, the molecular-level interplay between active sites and catalytic function still remains qualitative or semiquantitative, ascribed to the difficulty and uncertainty in elucidating the nature of active sites for its controllable manipulation. Hence, bridging the microscopic properties of active sites and the macroscopic catalytic performance, that is, microscopic-to-macroscopic transition, to afford a quantitative description is intriguing yet challenging, and progress toward this promises to revolutionize catalyst design and preparation.In this Account, we propose mesokinetics modeling, for the first time enabling a quantitative description of active site characteristics and the related mechanistic information, as a versatile tool to guide rational catalyst design. Exemplified by a pseudo-zero-order reaction, the kinetics derivation from the Pt particle size-sensitive catalytic activity and size-insensitive activation energy suggests only one type of surface site as the dominant active site, in which the Pt(111) with almost unchanged turnover frequency (TOF₁₁₁) is further identified as the dominating active site. Such a method has been extended to identify and quantify the number (N_i) of active sites for various thermo-, electro-, and photocatalysts in chemical synthesis, hydrogen generation, environment application, etc. Then, the kinetics derivation from the kinetic compensation effects suggests a thermodynamic balance between the activation entropy and enthalpy, which exhibit linear dependences on Pt charge. Accordingly, the Pt charge can serve as a catalytic descriptor for its quantitative determination of TOF_i. This strategy has been further applied to Pt-catalyzed CO oxidation with nonzero-order reaction characteristic by taking the site coverages of surface species into consideration.Hence, substituting the above statistical correlations of N_i and TOF_i into the rate equation R = ∑N_i × TOF_i offers the mesokinetics model, which can precisely predict catalytic function and screen catalysts. Finally, based on the disentanglement of the factors underlying Pt electronic structures, a de novo strategy, from the interfacial charge distribution to reaction mechanism, kinetics, and thermodynamics parameters of the rate-determining step, and ultimately catalytic performance, is developed to map the unified mechanistic and kinetics picture of reaction. Overall, the mesokinetics not only demonstrates much potential to elucidate the quantitative interplay between active sites and catalytic activity but also provides a new research direction in kinetics analysis to rationalize catalyst design.

Ultrahigh Metal Content Carbon-Based Catalyst for Efficient Hydrogenation of Furfural: The Regulatory Effect of Glycerol

The development of high-content non-noble metal nanocatalysts is important for multiphase catalysis applications. However, it is a challenge to solve the agglomeration in the preparation of high-content metal catalysts. In this paper, a carbon-based catalyst (Co@CN-G-600) with 71.28 wt % cobalt metal content was prepared using a new strategy of gas-phase carbon coating assisted by glycerol. The core of this strategy is to maintain the spacing of metallic cobalt by continuous replenishment of dissociated ligands during pyrolysis over gas-phase glycerol. This approach is also applicable to other non-noble metals. When Co@CN-G-600 was further used as a catalyst for the selective hydrogenation of furfural (FF) to prepare furfuryl alcohol (FOL), the yield of FOL was >99.9% under mild conditions of 80 °C, compared to only 8.23% catalytic yield at up to 130 °C for Co@CN-600 without glycerol. The excellent catalytic performance mainly lies in the fact that the introduction of glycerol modulates the size effect, electronic effect, and acidic site intensity of the high-content Co catalyst, which promotes the activation of FF and hydrogen. Meanwhile, the optimized specific surface area and pore structure by glycerol improve the accessibility of high-density active sites and promote more efficient mass transfer. In addition, the introduction of glycerol produced a graphitic carbon layer encapsulation structure relative to Co@CN-600, which substantially improved the cycling stability of the catalyst. This study resolves the paradox of high content and high dispersion of non-noble metal catalysts in the synthesis process and provides a general pathway and example for the preparation of stable high-content metal catalysts.